Laser spectroscopy on the hyperfine structure and isotope shift of sympathetically cooled ${}^{229}$Th${}^{3+}$ ions

The hyperfine structure of ${}^{229}$Th${}^{3+}$ ions in the nuclear ground state is investigated via laser spectroscopy of trapped Th${}^{3+}$ ions that are sympathetically cooled by laser-cooled ${}^{88}$Sr${}^{+}$ ions in a linear Paul trap. The isotope shift to ${}^{230}$Th${}^{3+}$ and the hyperfine constants for the magnetic dipole (A) and electric quadrupole (B) interactions for the 5F${}_{5\mathrm{/}2}$ and 6D${}_{5\mathrm{/}2}$ electronic states of ${}^{229}$Th${}^{3+}$ are determined. These measurements provide nuclear moments of ${}^{229}$Th with reduced uncertainty and serve as a preparation for improved hyperfine spectroscopy of the 8.4 eV nuclear isomeric state in ${}^{229}$Th${}^{3+}$ ions.